#include <stdio.h>
#include <math.h>
int main()
{
     
  double a,b,c,s,area; 
  printf("Input abc:");
  scanf("%lf %lf %lf",&a,&b,&c);
  
  if(a+b>c&&a+c>b&&b+c>a)
  {
  	s=(a+b+c)/2;
  	area=sqrt(s*(s-a)*(s-b)*(s-c));
  	printf("area=%.2f\n",area);
  }
  else
  {
  	printf("Not a triangle.\n");
  
  }	
  return 0;
}
  
   
